A sensitive and accurate method to simultaneously measure uric acid and creatinine in human saliva by using LC-MS/MS

A UOx@HMnO2 biozyme-nanozyme driven electrochemical platform for specific uric acid bioassays

Uric acid (UA) is a key end product of purine metabolism in the human body, and its abnormal levels are associated with many diseases, so accurate monitoring is essential. Existing detection methods have many limitations. For example, chromatography is cumbersome, time-consuming, and not cost-effective, while serum uric acid analysis requires specialized equipment and venous blood collection. In the field of uric acid sensors, electrochemical detection is commonly used but prone to interference, and nanomaterials offer improvements but are complicated to modify. To better block interference via an easily-made nanocomposite-based system, in this study, MnO2 with peroxidase-mimicking activity was used as a protective shell to encapsulate natural uric acid oxidase (UOx), realizing a good combination of nanozymes and biocatalysts. UOx can selectively catalyze UA and generate H2O2, and the MnO2 nanozymes can make up for the insufficiency of UOx, and the two main components synergistically enhance the activity of UOx@HMnO2, resulting in ultra-high performance. This provides a simple and general method for the preparation of efficient hybridized biocatalysts in the fields of biosensors and biocatalysis. The detection limit of the fabricated uric acid sensor is as low as 0.74 μM, and the concentration of the actual sample is consistent with that of mass spectrometry, which provides a means of non-invasive detection of uric acid with high sensitivity, high specificity and good accuracy.

Colorimetric and electrochemical dual-mode uric acid determination utilizing peroxidase-mimicking activity of CoCu bimetallic nanoclusters

We present the preparation of CoCu bimetallic nanoclusters (Co@Cu-BNCs) by a hydrothermal and one-step pyrolysis method to build a colorimetric and electrochemical dual-mode sensing platform for uric acid (UA) detection. In the presence of H2O2, Co@Cu-BNCs with peroxidase-mimicking activity may convert colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue-colored oxidized TMB (oxTMB). However, due to the inhibitory effect of uric acid (UA) on the oxidation process of TMB, the characteristic absorption peak intensity of oxTMB decreased when UA was added into a mixed solution. In this approach, a colorimetric assay platform for the detection of UA was demonstrated, with a linear range of 0.1-195 μM and a low limit of detection of 0.06 μM (S/N ratio of 3). In addition, an even wider detection range is achieved in the electrochemical method, due to the pronounced electrocatalytic activity of Co@Cu-BNCs. The surface of the glassy carbon electrode was modified with Co@Cu-BNCs to build an electrochemical sensor for detecting UA. The sensor achieves a wider linear range from 2 to 1000 μM and a limit of detection of 0.61 μM (S/N ratio of 3). Moreover, the detection of UA in a human serum sample showed satisfactory results. The results proved that the colorimetric and electrochemical dual-mode detection platform was sensitive, convenient and accurate.

Single-cell transcriptomics reveals variations in monocytes and Tregs between gout flare and remission

Gout commonly manifests as a painful, self-limiting inflammatory arthritis. Nevertheless, the understanding of the inflammatory and immune responses underlying gout flares and remission remains ambiguous. Here, based on single-cell RNA-Seq and an independent validation cohort, we identified the potential mechanism of gout flare, which likely involves the upregulation of HLA-DQA1+ nonclassical monocytes and is related to antigen processing and presentation. Furthermore, Tregs also play an essential role in the suppressive capacity during gout remission. Cell communication analysis suggested the existence of altered crosstalk between monocytes and other T cell types, such as Tregs. Moreover, we observed the systemic upregulation of inflammatory and cytokine genes, primarily in classical monocytes, during gout flares. All monocyte subtypes showed increased arachidonic acid metabolic activity along with upregulation of prostaglandin-endoperoxide synthase 2 (PTGS2). We also detected a decrease in blood arachidonic acid and an increase in leukotriene B4 levels during gout flares. In summary, our study illustrates the distinctive immune cell responses and systemic inflammation patterns that characterize the transition from gout flares to remission, and it suggests that blood monocyte subtypes and Tregs are potential intervention targets for preventing recurrent gout attacks and progression.

Purine Metabolism Dysfunctions: Experimental Methods of Detection and Diagnostic Potential

Purines, such as adenine and guanine, perform several important functions in the cell. They are found in nucleic acids; are structural components of some coenzymes, including NADH and coenzyme A; and have a crucial role in the modulation of energy metabolism and signal transduction. Moreover, purines have been shown to play an important role in the physiology of platelets, muscles, and neurotransmission. All cells require a balanced number of purines for growth, proliferation, and survival. Under physiological conditions, enzymes involved in purines metabolism maintain a balanced ratio between their synthesis and degradation in the cell. In humans, the final product of purine catabolism is uric acid, while most other mammals possess the enzyme uricase that converts uric acid to allantoin, which can be easily eliminated with urine. During the last decades, hyperuricemia has been associated with a number of human extra-articular diseases (in particular, the cardiovascular ones) and their clinical severity. In this review, we go through the methods of investigation of purine metabolism dysfunctions, looking at the functionality of xanthine oxidoreductase and the formation of catabolites in urine and saliva. Finally, we discuss how these molecules can be used as markers of oxidative stress.

Non-enzymatic electrochemical detection of creatinine based on a glassy carbon electrode modified with a Pd/Cu2O decorated polypyrrole (PPy) nanocomposite: an analytical approach

The major constraints of standard enzymatic biosensors are poor long-term storage stability and high cost. Hence, there is extensive research towards fabrication of reliable enzymeless biosensors based on nanomaterials. In this paper, we present the development of an enzymeless electrochemical biosensor for highly precise detection of creatinine. This involves the use of a simple yet effective alternative to the commonly utilized Pd/Cu₂O/PPy nanocomposite, which was characterized by different analytical methods. The present electrochemical sensor provides a wide detection range (0.1 to 150 μM), low detection limit (0.05 μM) and high sensitivity (0.207 μA), and is capable of detecting the creatinine level in human urine samples, which are inexpensive. The results are reproducible, and the sensor is stable. The sensor demonstrates good electrocatalytic activity and selectivity towards the detection of creatinine in the presence of various other similar biological entities. When compared to other existing counterparts, the electrocatalytic behaviour of the present sensor is comparable, if not better. So, the present electrochemical sensor for creatinine might be employed as a long-term diagnostic alternative.

Association between serum uric acid levels and simple renal cyst risk in a nondiabetic population: A nested case-control study

BACKGROUND

Previous studies have found a relationship between hypertension or cardiovascular disease and simple renal cysts (SRCs) in health check-up population, but SRCs incidence is still controversially associated with serum uric acid (SUA) concentration in the nondiabetic participants. In this single-centre nest case-control study, serum uric acid levels were examined in relation to the incidence of SRCs in nondiabetic individuals.

METHOD

Participants who underwent at least two renal ultrasound examinations with an interval of more than 12 months were enrolled. The results of clinical examinations, laboratory tests and abdominal ultrasound tests were recorded for each participant and analysed in this retrospective observation study.

RESULT

A total of 144 control and 144 SRC patients were ultimately confirmed and included in further analysis. Hyperuricaemia (OR 2.846, 95% CI 1.519-5.332, p = 0.001) was significantly correlated with SRC formation according to multivariable analysis. In both the male and female groups, SRC patients had significantly higher serum uric acid levels compared with control subjects. In 54 SRC patients with cyst puncture, the serum uric acid concentration was positively correlated with the uric acid concentration in cyst fluid (r = 0.6144, p < 0.0001). The serum uric acid concentration was positively correlated with the maximum cyst diameter in the SRC patients (r = 0.4531, p < 0.0001).

CONCLUSION

In a nondiabetic population, hyperuricaemia was significantly independently associated with a higher SRCs incidence. In SRC participants with cyst puncture, the SUA level had a significantly positive correlation with the uric acid level in cyst fluid. In SRC patients, the SUA level had a significantly positive correlation with cyst maximum diameter.

Can salivary lactate be used as an anaerobic biomarker?

Background

Salivary lactate has been suggested as a non-invasive anaerobic biomarker in sports medicine for decades, yet has not been widely applied until now. This study aimed to explore possible issues related to its application and suggest directions for future method improvement.

Methods

A liquid chromatography-mass spectrometry (LC-MS) method for the determination of salivary lactate was developed, validated and applied on saliva samples collected from a group of professional sprinters (n = 20). The samples were collected via chewing a cotton ball for one minute and centrifuging it afterwards. The evaluation included variation with mouth rinse times, consistency at different sampling times, change after treadmill or cycle ergometer trainings, and association with blood lactate. Sample sizes were calculated prior to the study. One-way analysis of variance (ANOVA), intra-class correlation coefficients (ICC) and relative standard deviation (RSD) were used to evaluate data variances. Pearson correlation was applied to show correlation between salivary and blood lactate. Effect sizes and power were calculated following ANOVA and correlation analyses.

Results

The RSD of the LC-MS method was 19.70%. Salivary lactate concentration was affected by mouth rinse times before sampling (ANOVA p = 0.025, η ² = 0.40, 1 - β = 0.99, ICC = 0.23, mean RSD of four sampling = 55.30%), and stabilized after mouth rinsing for three times. The concentrations at resting state across three weeks were consistent at group level (ANOVA p = 0.57, η ² = 0.03, 1 - β = 0.20), but varied greatly individually (ICC = 0.22, mean RSD = 56.16%). Salivary lactate level significantly increased after treadmill and cycle ergometer trainings (ANOVA p = 0.0002, η ² = 0.46, 1 - β = 0.9999 and ANOVA p = 0.0019, η ² = 0.40, 1 - β = 0.9993, respectively), and displayed positive correlation with blood lactate concentration (r = 0.61, p = 0.0004, 1 - β = 0.9596). Significant difference between male and female participants was observed in none of the tests conducted in this study.

Discussion

Salivary lactate was found to be a potential anaerobic biomarker. However, reproducible methods for sample collection and analysis, as well as more knowledge on the secretion mechanism and pattern of salivary lactate are required to make it a practical anaerobic biomarker.

Developing Activated Carbon Veil Electrode for Sensing Salivary Uric Acid

The paper describes the development of a carbon veil-based electrode (CVE) for determining uric acid (UA) in saliva. The electrode was manufactured by lamination technology, electrochemically activated and used as a highly sensitive voltammetric sensor (CVEact). Potentiostatic polarization of the electrode at 2.0 V in H2SO4 solution resulted in a higher number of oxygen and nitrogen-containing groups on the electrode surface; lower charge transfer resistance; a 1.5 times increase in the effective surface area and a decrease in the UA oxidation potential by over 0.4 V, compared with the non-activated CVE, which was confirmed by energy dispersive X-ray spectroscopy, electrochemical impedance spectroscopy, chronoamperometry and linear sweep voltammetry. The developed sensor is characterized by a low detection limit of 0.05 µM and a wide linear range (0.09-700 µM). The results suggest that the sensor has perspective applications for quick determination of UA in artificial and human saliva. RSD does not exceed 3.9%, and recovery is 96-105%. UA makes a significant contribution to the antioxidant activity (AOA) of saliva (≈60%). In addition to its high analytical characteristics, the important advantages of the proposed CVEact are the simple, scalable, and cost-effective manufacturing technology and the absence of additional complex and time-consuming modification operations.

Chromatographic method for the determination of inflammatory biomarkers and uric acid in human saliva

Determination of concentration of biomarkers of the activation of immune system, uric acid, and creatinine in the saliva can be useful tool for the diagnosis and monitoring of early manifestations of diseases such as malignant, inflammatory, and periodontal disorders. We have developed and validated a high-performance liquid chromatographic method coupled with fluorescence and diode array detection for the separation and quantification of neopterin, tryptophan, creatinine, uric acid, and kynurenine in the human saliva. A separation of these analytes was achieved within 9 min by using second-generation monolithic stationary phase and elution with phosphate buffer. The present method involves very simple sample preparation requiring small amount of sample matrix. The internal standard 3-nitro-l-tyrosine was used for a more precise quantification. The sensitivity of the present method was demonstrated with lower limits of quantification of 0.6 × 10^-3 μmol/L for neopterin, 0.725 μmol/L for tryptophan, 0.12 μmol/L for creatinine, 0.18 μmol/L for uric acid, and 0.135 μmol/L for kynurenine. The method was validated with 67 real-life saliva samples collected from patients suffering from breast, ovarian, colorectal, and renal cancer, and 19 saliva samples from patients with periodontal diseases and allowed monitoring of inflammatory response.

Pentacyanoammineferrate-Based Non-Enzymatic Electrochemical Biosensing Platform for Selective Uric Acid Measurement

The electrochemical-based detection of uric acid (UA) is widely used for diagnostic purposes. However, various interfering species such as ascorbic acid, dopamine, and glucose can affect electrochemical signals, and hence there is an outstanding need to develop improved sensing platforms to detect UA with high selectivity. Herein, we report a pentagonal mediator-based non-enzymatic electrochemical biosensing platform to selectively measure UA in the presence of interfering species. The working electrode was fabricated by electrodepositing polymerized 1-vinylimidazole (PVI), which has an imidazole ligand, onto indium tin oxide (ITO), and then conjugating nickel ions to the PVI-coated ITO electrode. Electrode performance was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements and integrated together with pentacyanoammineferrate, which can bind to the amine groups of UA and function as an electron transferring mediator. The experimental results showed a wide linear range of UA concentration-dependent responses and the multi-potential step (MPS) technique facilitated selective detection of UA in the presence of physiologically relevant interfering species. Altogether, these findings support that pentacyanoammineferrate-based non-enzymatic electrodes are suitable biosensing platforms for the selective measurement of UA, and such approaches could potentially be extended to other bioanalytes as well.

Electrochemical dual signal sensing platform for the simultaneous determination of dopamine, uric acid and glucose based on copper and cerium bimetallic carbon nanocomposites

A highly sensitive electrochemical sensor for the simultaneous dual signal determination of dopamine (DA), uric acid (UA) and glucose (Glu) has been obtained using nanocomposites based on the copper and cerium bimetallic nanoparticles and carbon nanomaterials of graphene and single-walled carbon nanotubes in the presence of Tween 20 (GR-SWCNT-Ce-Cu-Tween 20) modified glassy carbon electrode. The surface morphology of the nanocomposites was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), and the electrochemical behavior of the sensor was investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) with potassium ferricyanide as probe. In the coexistence system of DA, UA and Glu, three clear and well-isolated voltammetric peaks were obtained by CV and differential pulse voltammetry (DPV), and oxidation peak currents of DA and UA are positively correlated with their concentrations respectively, while the peak current of Glu is negatively correlated with its concentration. Linearity was obtained in the ranges of 0.1-100 µM for dopamine, 0.08-100 µM for uric acid and 1-1000 µM for glucose with DPV, and the detection limits (S/N = 3) of 0.0072 µM, 0.0063 µM, and 0.095 µM for DA, UA and Glu, respectively. The method was successfully applied to the determination of DA, UA and Glu in blood serum samples, which provided a reference for further sensor research.

Non-invasive determination of uric acid in human saliva in the diagnosis of serious disorders

This review summarizes and critically evaluates the published approaches and recent trends in sample pre-treatment, as well as both separation and non-separation techniques used for the determination of uric acid (UA) in saliva. UA is the final product of purine nucleotide catabolism in humans. UA concentrations in biological fluids such as serum, plasma, and urine represent an important biomarker of diseases including gout, hyperuricemia, or disorders associated with oxidative stress. Previous studies reported correlation between UA concentrations detected in saliva and in the blood. The interest in UA has been increasing during the past 20 years from a single publication in 2000 to 34 papers in 2019 according to MEDLINE search using term "uric acid in saliva". The evaluation of salivary UA levels can contribute to non-invasive diagnosis of many serious diseases. Increased salivary UA concentration is associated with cancer, HIV, gout, and hypertension. In contrast, low UA levels are associated with Alzheimer disease, progression of multiple sclerosis, and mild cognitive impairment.

Ready for TDM: Simultaneous quantification of amikacin, vancomycin and creatinine in human plasma employing ultra-performance liquid chromatography-tandem mass spectrometry

BACKGROUND

Amikacin (AMI) and vancomycin (VAN) are antibiotics largely used in intensive care in the empiric treatment of severe infections by multi-resistant gram-negative and gram-positive bacteria. AMI and VAN are eliminated untransformed by glomerular filtration, showing depuration ratio highly correlated with creatinine (CRE) clearance. AMI, VAN and CRE are highly polar structures, presenting poor retention in reversed-phase liquid chromatography when using conventional stationary phases.

OBJECTIVE

This study aimed to develop and validate a simple UPLC-MS/MS method for simultaneous determination of AMI, VAN, and CRE in human plasma for therapeutic drug monitoring.

RESULTS

Samples were prepared by protein precipitation, followed by dilution. Heptafluorobutyric acid (HFBA) was added to the mobile phase at low concentration (0.01%), and separation was performed in an ultra-performance reversed-phase column (particle diameter of 1.8 μm). These conditions allowed retention times of 0.92, 0.93, 2.12, 2.17 and 2.27 min for CRE, CRE-D3, AMI, KAN and VAN, respectively. The assay was linear from 0.5 to 100 mg L^-1 for AMI and VAN and 5 to 100 mg L^-1. Precision, accuracy and stability assays were acceptable according to bioanalytical validation guidelines. Suitable results. Matrix effects were in the range of +10.5 to +11.6% for AMI, -4.3 to -4.5% for VAN, and - 1.7 to +0.7 for CRE.

CONCLUSION

The first assay for the simultaneous determination of AMI, VAN and CRE in plasma by liquid chromatography-tandem mass spectrometry was reported. This assay allows the obtention of the necessary analytical data for the clinical application of population pharmacokinetic methods for therapeutic drug monitoring of AMI and VAN.

A simplified, rapid LC-MS/MS assay for serum and salivary creatinine

In routine clinical laboratories, serum creatinine is typically measured on automated analyzers using colorimetric or enzymatic assays, which are both susceptible to interferences that can lead to incorrect measurement. Here, we present a straightforward and rapid LC-MS/MS assay for serum creatinine using methanol extraction, with separation performed using a strong cation exchange column. Results from this newly developed method were compared against those from an automated Abbott Architect kinetic Jaffe method. We also assessed the effect of bilirubin and glucose, as interferants, on both methods. Our LC-MS/MS assay has a run time of 1.1 min, uses a relatively small sample volume of 10 µL and has a within-batch imprecision of 1.1-1.8% at the concentrations tested, which is within the range necessary for routine clinical use. Recovery from serum samples spiked with creatinine was >95%, and glucose and bilirubin were not found to interfere in the assay. Glucose was observed to significantly interfere in the kinetic Jaffe method, while bilirubin had a variable effect. We also determined that creatinine can be measured from saliva using our method, and that salivary concentrations are, on average, 15% of those in serum. This assay provides an alternative for patient sample analysis where interference is expected in routine creatinine methods.

Plasma profiling of amino acids distinguishes acute gout from asymptomatic hyperuricemia

Gout and hyperuricemia are highly prevalent metabolic diseases caused by high level of uric acid. Amino acids (AAs) involve in various biochemical processes including the biosynthesis of uric acid. However, the role of AAs in discriminating gout from hyperuricemia remains unknown. Here, we report that the plasma AAs profile can distinguish acute gout (AG) from asymptomatic hyperuricemia (AHU). We established an LC-MS/MS-based method to measure the plasma AAs without derivatization for the AG and AHU patients, and healthy controls. We found that the plasma profiling of AAs separated the AG patients from AHU patients and controls visually in both principal component analysis and orthogonal partial least-squares discriminant analysis (OPLS-DA) models. In addition, L-isoleucine, L-lysine, and L-alanine were suggested as the key mediators to distinguish the AG patients from AHU and control groups based on the S-plot analysis and variable importance in the projection values in the OPLS-DA models, volcano plot, and the receiver operating characteristic curves. In addition, the saturation of monosodium urate in the AA solutions at physiologically mimic status supported the changes in plasma AAs facilitating the precipitation of monosodium urate. This study suggests that L-isoleucine, L-lysine, and L-alanine could be the potential markers to distinguish the AG from AHU when the patients have similar blood levels of uric acid, providing new strategies for the prevention, treatment, and management of acute gout.